Project Summary/Abstract There is a large subgroup of older foster youth who have limited support network capacity and stability, with related limitations on adolescent development, social functioning, and overall mental health and well-being. This population has elevated behavioral challenges as they exit foster care, but they are less likely engage in formal services and have fewer informal supports to rely on in young adulthood. To improve the mental health and well-being of this population in young adulthood, the practice field needs innovative strategies to address depleted social networks while these young people are still being served by the child welfare system. However, there is no articulated framework linking measurable support network characteristics with indicated practice strategies to facilitate support and community integration in ways that can improve health and well-being (for example, by increasing formal service engagement or informal help-seeking). This project will result in a testable intervention for young people in foster care who are at risk for mental health and/or social adjustment challenges in young adulthood. The long-term goal if this effort is to disseminate an effective group-based support network enhancement model for delivery as part of the regular child welfare system service array. The short-term goal is to use the rigorous Intervention Mapping (IM) protocol to articulate a theory of change for foster youth support network enhancement, and to design a feasible intervention to address measurable objectives, in collaboration with mental health and child welfare stakeholders and with young people with lived experience. This will be accomplished through the following specific aims: (1) conduct rigorous problem analysis, including a systematic literature review of problem determinants and directed content analysis of secondary data (N=22), to specify problem determinants at the individual and socioecological levels and to identify related proximal program objectives; (2) explicate a theory of change model for the program objectives, and design a program to deliver practical change strategies in the expected implementation context; (3) pre-test the program design with the target population of youth in foster care (N=40) and with their service providers (N=40) to evaluate usability and feasibility in various service regions; and, (4) refine the model and materials for implementation and future efficacy testing as part of the Independent Living Program (ILP) system serving foster youth across the country. Developing effective programming to assess and address support network deficits for subgroups of foster youth while they are still being served by the child welfare systems can help bridge the transition from formal services to informal support in ways that improve young adult mental health and well-being. This project applies established network theory to address the unique socioecological challenges experienced by system-involved youth, and links empirical knowledge to practical strategies (e.g., network assessment, relational skill-building, near-peer support) for use in the field.